Hi.

My Local Authority needs calcs for a steel column I'm proposing in my extension.

It will be approx 2.2M tall, 80x80mm square x 5mm wall. Axial loading (dead load + imposed load from snow) will be maximum of (from a rough calc) 2.5KN. I have no access to BS5950 without buying it, but Corus Steels seem to have all the tables where I can look up Axial load capacity and something called d/t ratio. I don't know where to work out buckling load, and I'm not quite sure what is meant by an axial load "capacity". I'm sure this need not be too complex.
-Any pointers?

As tony says. If 2.5 is all you're carrying. You're at about 1% of its capacity.

Is there a reason why you are not employing a structural engineer?
I used to do architectural drawings and for simple jobs they didn't charge much more than £100, although this was some time ago.
I obviously don't know the situation but 2.5kN (250kg) is a tiny load, are you sure you've worked it out properly?
I thought basic imposed domestic floor loading was 1.5kN/m2, snow loading 0.75kN/m2. Then you have to multiply these by safety factors, so 2.5kN doesn't amount to much.

Thanks guys, sorry for the delay replying, I do appreciate the assistance.

Suffice to say that I got my application accepted after burning much midnight oil last week- hence not replying here.

I can also say publicly IG Lintels have been very helpful. Oh and neilu, for the record, yes sorry, typo put my dot in the wrong place and indeed 2.5KN is indeed a small load! (It's only a small job, but approx a factor of 10 out. In fact it was a corner post to support a single storey corner extension with wrap-round window and a lightweight roof). Eventual post was hugely over speced (as I suspected, be everyone is happy now). QED.